The NEKOMIMI Cooling Technology: Cooling Holes With Ears for High-Efficient Film Cooling

2011 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Experimental Investigations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
High Efficient ◽  
Cylindrical Holes ◽  
Cooling Technology ◽  
Lift Off ◽  
Cooling Air

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter-rotating vortices (CRV) in the cooling jets and lead to jet lift-off effects. Thus, the film-cooling effectiveness is reduced soon behind the cooling air ejection through the holes. Due to that basic understanding, different technologies for improving film cooling have been developed. Some of them focus on establishing anti-counter-rotating vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the double-jet film cooling (DJFC), invented by the authors, where the special arrangement of two cylindrical holes lead to a cooling jet with such an anti-vortex system. However, beside the advantage that the holes are simple cylindrical holes, one disadvantage is that appropriate supply with cooling air for both holes is sometimes difficult to be established in real configurations. Thus, the authors have followed the idea to transfer the original double-jet film cooling principle to a special configuration with merged holes. Thus, in that case only one air supply is necessary but the anti-vortex effect has been preserved. The derived cooling technology has been named NEKOMIMI technology. The paper explains the principle of that technology. Results from experimental investigations including film cooling effectiveness measurements for the new technology are presented. The results are compared to conventional cooling hole configurations showing the tremendous positive effect in reaching highest film cooling effectiveness for the new configuration at M = 1.5 and partly for M = 1. Numerical investigations for the M = 1.5 case indicate that the existence of the ACRV is the likely reason for the enhanced cooling performance of the new configuration.

Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 2 — Hot Gas Flow Conditions

2013 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Azadeh Kasiri ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Gas Flow ◽  
Flow Conditions ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Hot Gas ◽  
High Efficient ◽  
Cooling Technology ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is common knowledge today that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-counter-rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for fabrication by advanced machining processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under hot gas flow conditions. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. The best configuration outperforms the basic configuration by more than 20% regarding the overall averaged adiabatic film cooling effectiveness.

A Parametric Study on the Influence of the Lateral Ejection Angle of Double-Jet Holes on the Film Cooling Effectiveness for High Blowing Ratios

2009 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Parametric Study ◽  
Film Cooling ◽  
Gas Turbines ◽  
Lateral Spreading ◽  
Experimental Investigations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Ejection Angle ◽  
Cooling Technology ◽  
Cooling Air

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. The reduction of the cooling air claims for an improved cooling technology, which assures the protection of the vane and blade airfoil from the hot mainstream flow. Consequently, it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices, which transport hot gas underneath the cooling jet and leads the cooling jet to lift off the surface. The double-jet film cooling technology represents a solution to establish an anti-kidney vortex, which prevents the double jet from lifting off the surface and raises the lateral spreading of the cooling air. This is achieved by a particular arrangement of simple cylindrical holes to each other. Additionally, the design of double-jet holes reduces significantly the effort of hole manufacturing compared to the effort of manufacturing a shaped hole design. Numerical investigations for blowing ratios from M = 0.5 up to M = 2 and experimental investigations in a test rig prove the proper film cooling ability of the double-jet film cooling technology. Furthermore, this paper presents a numerical parametric study of the double jet film cooling technology. The influence of the lateral ejection angle on the distribution of the cooling film is calculated and analyzed for the blowing ratios of M = 1, M = 1.5 and M = 2. It can be shown that an even higher film cooling effectiveness is reached with the use of the double-jet film cooling technology by an improvement of the hole positions and hole angles than in previous investigations.

Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 1 — Ambient Air Flow Conditions

2013 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Frederieke Reiners ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Air Flow ◽  
Ambient Air ◽  
Flow Conditions ◽  
Test Rig ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Technology ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is a today common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for manufacturing even by advanced manufacturing processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations much easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under ambient air flow conditions similar to conditions for a wind tunnel test rig. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. A set of most promising configurations has been also investigated experimentally in the test rig. The best configuration outperforms the basic configuration by 17% regarding the overall averaged adiabatic film cooling effectiveness under the experimental conditions.

Experimental and Numerical Investigations of the NEKOMIMI Film Cooling Technology

2012 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Film Cooling ◽  
Gas Turbines ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Numerical Investigations ◽  
Hot Gas ◽  
Cooling Technology ◽  
Lift Off ◽  
Cooling Air

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter rotating vortices (CRV) in the cooling jets and lead to jet liftoff effects. Novel film cooling technologies focus on establishing anti-counter-rotating-vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the NEKOMIMI film cooling, which is derived from the original double-jet film cooling (DJFC).

Numerical Analysis on the Leading Edge Film Cooling of Bifurcation Holes for Gas Turbine Blade

2021 ◽  
Author(s):  
Zhonghao Tang ◽  
Gongnan Xie ◽  
Honglin Li ◽  
Wenjing Gao ◽  
Chunlong Tan ◽  
...  
Keyword(s):  
Turbine Blade ◽  
Film Cooling ◽  
Turbulence Models ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
Lift Off

Abstract Film cooling performance of the cylindrical film holes and the bifurcated film holes on the leading edge model of the turbine blade are investigated in this paper. The suitability of different turbulence models to predict local and average film cooling effectiveness is validated by comparing with available experimental results. Three rows of holes are arranged in a semi-cylindrical model to simulate the leading edge of the turbine blade. Four different film cooling structures (including a cylindrical film holes and other three different bifurcated film holes) and four different blowing ratios are studied in detail. The results show that the film jets lift off gradually in the leading edge area as the blowing ratio increases. And the trajectory of the film jets gradually deviate from the mainstream direction to the spanwise direction. The cylindrical film holes and vertical bifurcated film holes have better film cooling effectiveness at low blowing ratio while the other two transverse bifurcated film holes have better film cooling effectiveness at high blowing ratio. And the film cooling effectiveness of the transverse bifurcated film holes increase with the increasing the blowing ratio. Additionally, the advantage of transverse bifurcated holes in film cooling effectiveness is more obvious in the downstream region relative to the cylindrical holes. The Area-Average film cooling effectiveness of transverse bifurcated film holes is 38% higher than that of cylindrical holes when blowing ratio is 2.

Double-Jet Ejection of Cooling Air for Improved Film-Cooling

2006 ◽  
Author(s):  
Karsten Kusterer ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Gas Flow ◽  
Operating Conditions ◽  
Cooling Effectiveness ◽  
Equal Distribution ◽  
Cooling Fluid ◽  
Film Cooling Effectiveness ◽  
Conventional Film ◽  
Cooling Technology

Film-cooling in gas turbines leads to aerodynamic mixing losses and reduced temperatures of the gas flow. Improvements of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount and by establishing a more equal distribution of the cooling fluid along the surface. It is well known that vortex systems in the cooling jets are the origin of reduced film-cooling effectiveness. For the streamwise ejection case, kidney-vortices result in a lift-off of the cooling jets; for the lateral ejection case, usually only one dominating vortex remains, leading to hot gas flow underneath the jet from one side. Based on the results of numerical analyses, a new cooling technology has been introduced by the authors, which reaches high film-cooling effectiveness as a result of a well-designed cooling hole arrangement for interaction of two neighbouring cooling jets (Double-jet Film-cooling DJFC). The results show that configurations exist, where an improved film-cooling effectiveness can be reached because an anti-kidney vortex pair is established in the double-jet. The paper aims on following major contributions: • to introduce the Double-jet Film-cooling (DJFC) as an alternative film-cooling technology to conventional film-cooling design. • to explain the major phenomena, which lead to the improvement of the film-cooling effectiveness by application of the DJFC. • to prove basic applicability of the DJFC to a realistic blade cooling configuration and present first test results under machine operating conditions.

Double-Jet Film-Cooling for Highly Efficient Film-Cooling With Low Blowing Ratios

2008 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Gas Turbines ◽  
Original Design ◽  
Long Distance ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Air ◽  
Very High

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness so that the available cooling air fulfils the cooling task even if the amount has been reduced. In particular, the cooling effort for the vanes and blades of the first stage in a modern gas turbine is very high. The task of the film-cooling is to protect the blade material from the hot gas attack to the surface. Unfortunately, aerodynamic mixing processes are enhanced by secondary vortices in the cooling jets and, thus, the film-cooling effectiveness is reduced shortly behind the cooling air ejection through the holes. By improvement of the hole positioning the negative interaction effects can be reduced. The Double-jet Film-cooling (DJFC) Technology invented by the authors is one method to reach a significant increase in film-cooling effectiveness by establishing an anti-kidney vortex pair in a combined jet from the two jets starting from cylindrical ejection holes. This has been shown by numerical investigations and application to an industrial gas turbine as reported in recent publications. Whereas the original design application has been for moderate and high blowing ratios, the present numerical investigation shows that the DJFC is also applicable for lower blowing ratios (0.5<M<1.0) with only slight modification of the geometry of the configuration. The anti-kidney vortex concept can also be established for the lower blowing ratios and, as a result, a very high film-cooling effectiveness is reached not only behind the ejection holes but also for a very long distance downstream (> 30 hole diameters).

Film Cooling Effectiveness Comparison Between Shaped- and Double Jet Film Cooling Holes in a Row Arrangement

2010 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Experimental Comparison ◽  
Comparison Study ◽  
Surface Cooling ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Shaped Hole ◽  
Cooling Air ◽  
Cooling Technique

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the needed cooling air amount. Consequently it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices which transport hot gas underneath the cooling jet and leads the cooling jet to lift off from the surface. Cooling performance is highly increased by using the shaped hole technique, which weakens the kidney vortex structure. However the formation of secondary flows can not completely be avoided by using shaped holes instead of cylindrical holes. Another promising film cooling technology is the double-jet film cooling, which prevents the cooling jet from lifting off the surface and raises the lateral spreading of the cooling air by generating an anti kidney vortex. This paper presents a comparison of the film cooling effectiveness between the shaped film cooling technique and the novel double jet film cooling technique for the high blowing ratios M = 1, M = 1.5 and M = 2. Various geometries of fan-shaped holes with lateral expansion angles of 10°, 14° and 18° are used for the comparison study. It can be shown that the shaped hole row arrangement provides higher cooling values in a slight region near to the hole exits, while the double jet film cooling technique shows a obvious cooling advantage in the further downstream area for high blowing ratios. Furthermore recent results of an on-going experimental comparison study between the double jet, trench and cylindrical technique are presented, which proves the advantage capability of the double jet film cooling.

Influence of Blowing Ratio on the Double-Jet Ejection of Cooling Air

2007 ◽  
Author(s):  
Karsten Kusterer ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Vortex Pair ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Secondary Vortices ◽  
Cooling Air ◽  
Combined Cooling

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness so that the available cooling air fulfils the cooling task even if the amount has been reduced. In particular, the cooling effort for the vanes and blades of the first stage in a modern gas turbine is very high. The task of the film-cooling is to protect the blade material from the hot gas attack to the surface. Unfortunately, aerodynamic mixing processes are enhanced by secondary vortices in the cooling jets and, thus, the film-cooling effectiveness is reduced shortly behind the cooling air ejection through the holes. By improvement of the hole positioning, the negative interaction effects can be reduced. One approach is the Double-jet Film-cooling (DJFC) Technology presented recently by the authors. It has been shown by numerical simulations that for a special and precise arrangement of two holes, the interaction of the secondary vortices can be used for a significant increase in film-cooling effectiveness. This is reached by establishing an anti-kidney vortex pair in a combined jet from two jets starting from two cylindrical ejection holes. The influence of the blowing ratio on the double-jet ejection is investigated numerically. The configurations of the double-hole arrangements have been investigated only for a relative high blowing ratio (M = 1.7). The present investigations focus on moderate blowing ratios (1.0 < M < 1.5) and on a higher blowing ratio of M = 2.0. It can be shown that also for moderate blowing ratios the anti-kidney vortex pair is generated in the combined cooling jet. Thus, high adiabatic film-cooling effectiveness can be reached also for the case with a moderate blowing ratio. The lateral distribution of the cooling air is reduced compared to the cases of higher blowing ratios (M = 1.7, M = 2.0).

A Three-Regime Based Method for Correlating Film Cooling Effectiveness for Cylindrical and Shaped Holes

2015 ◽  
Author(s):  
Lieke Wang ◽  
Mats Kinell ◽  
Hossein N. Najafabadi ◽  
Matts Karlsson
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Gas Turbines ◽  
Density Ratio ◽  
Transition Regime ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

To cope with high temperature of the gas from combustor, cooling is often used in the hot gas components in gas turbines. Film cooling is one of the effective methods used in this application. Both cylindrical and fan-shaped holes are used in film cooling. There have been a number of correlations published for both cylindrical and fan-shaped holes regarding film cooling effectiveness. Unfortunately there are no definitive correlations for either cylindrical or fan-shaped holes. This is due to the nature of the complexity of film cooling where many factors influence its performance, e.g., blowing ratio, density ratio, surface angle, downstream distance, expansion angle, hole length, turbulence level, etc. A test rig using infrared camera was built to test the film cooling performance for a scaled geometry from a real nozzle guide vane. Both cylindrical and fan-shaped holes were tested. To correlate the experimental data, a three-regime based method was developed for predicting the film cooling effectiveness. Based on the blowing ratio, the proposed method divides the film cooling performance in three regimes: fully attached (or no jet lift-off), fully jet lift-off, and the transition regime in between. Two separate correlations are developed for fully attached and full jet lift-off regimes, respectively. The method of interpolation from these two regimes is used to predict the film cooling effectiveness for the transition regime, based on the blowing ratio. It has been found this method can give a good correlation to match the experimental data, for both cylindrical and fan-shaped holes. A comparison with literature was also carried out, and it showed a good agreement.

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